Dynamical evolution equations, e.g. Langevin dynamics [1]}, [2]} and various relaxational models [3]}, [4]}, are usually used in order to describe the relaxation from nonequilibrium to equilibrium and obtain the effects of nonequilibrium in the QCD critical region. The dynamical evolution equations of nonequilibrium systems in Refs. [3]}, [4]} describe the crossover side of the critical point. They incorporate the fluctuation and dissipation. The intrinsic thermal fluctuations drive the system constantly out of equilibrium. Dissipative processes balance the impact of fluctuations. Equilibrium is a result of the balance between dissipation and fluctuations. Near a critical point, the fluctuation is significantly enhanced and equilibrium is hard to reach in a limited time.
